The invention relates to a method of operating an internal combustion engine wherein a desired intake air pressure is determined as a function of a desired load and set by means of an air supply device controlling the air flow to the cylinders of the engine.
The document DE 195 30 274 A1 discloses a method of controlling an internal combustion engine with fully variable valve drive, which permits the opening and closing of the gas exchange valves independently of one another. The desired load, which results from the position of the acceleration pedal and the momentary slope inclination or which originates from an electronic driving-dynamics control arrangement, is converted by means of a fuel control unit into an amount of fuel to be injected. Injection timing and ignition timing are to be determined using performance graphs. The corresponding amount of fresh air is supplied to the combustion chambers of the internal combustion engine by means of the activation of the gas exchange valves.
In order to regulate the required amount of fresh air, the amount of air actually introduced is determined with the aid of an air mass meter disposed in the intake tract of the internal combustion engine. It is however disadvantageous in this case that the air mass meter reacts comparatively sluggishly, that is, it reacts slowly compared to the movement to be performed by the gas exchange valves. Load changes, which affect the valve stroke of the gas exchange, are implemented by the gas exchange valves without a time delay. The air mass meter, reacting comparatively sluggishly, lags behind the fast reaction of the gas exchange valves, so that measured values of the air mass meter do not correspond to the actual conditions in the intake tract during dynamic changes. As a consequence, for example, during high accelerations or decelerations, a fuel/air ratio deviating from the stoichiometric ratio may be established.
It is the object of the invention to provide for an improved response behavior of internal combustion engines during load changes.
In a method for operating an internal combustion engine as a function of a desired load, wherein a desired pressure in the intake pipe of the internal combustion engine is determined and is set by means of an air supply device, the ignition timing, the beginning of fuel injection and the duration of fuel injection values are determined in accordance with a predetermined relationship as a function of the desired load and the values are supplied as actuating signals to actuating elements by which the ignition and the fuel injection are adjusted to improve the engine response behavior.
With the novel method, both of the parameters which determine ignition and the parameters which determine injection, such as ignition timing, beginning of fuel injection and duration of fuel injection are determined as a function of the predetermined load, which depends, in particular, on the accelerator pedal position and also, if appropriate on manipulated variables of a driving-dynamics performance graph. These parameters which determine the ignition and the injection timing, are usually already determined for determining the amount of air to be supplied to the internal combustion engine and are thus available in the engine control unit. The ignition timing the beginning of fuel injection and the duration of fuel injection are supplied as actuating signals to actuating elements by which the ignition and the injection are performed.
With the method according to the invention, it is possible for the first time for both, the air side and the fuel side of an internal combustion engine, to be set by means of a common parameterxe2x80x94the desired load. This results in a simpler design of the engine controller and regulator and also of the units used in the internal combustion engine, since a common parameter is used to control both the air supply and the fuel supply, and respectively, the ignition. A further advantage resides in the fast dynamics of an internal combustion engine operated in the manner according to the invention. Since there is no longer a need for an air mass meter or a similar measuring element in the intake tract, measurement-dictated delays are eliminated. Accordingly, the internal combustion engine can react more rapidly to load changes, and mixture formation errors are reduced. Corrections in the event of deviation from the stoichiometric fuel/air ratio can, if appropriate, be compensated for by means of the lambda control. Furthermore, it is also possible to control engine knocking so as to prevent damaging engine knocking by adjusting the ignition timing.
The novel method is preferably used in internal combustion engines which have an adjustable air supply device for supplying combustion air to the cylinders, in particular adjustable gas exchange valves or, alternatively, both adjustable gas exchange valves and a throttle valve. The engines are furthermore equipped with an engine control unit, in which, as a function of input signals characterizing the operating state of the internal combustion engine, actuating signals are generated in accordance with stored performance graphs. The signals are fed to actuating elements of the internal combustion engine, in particular for the ignition and the fuel injection and also the air supply devices. Electromagnetic, variably adjustable gas exchange vales are preferably used. However, mechanically adjustable gas exchange valves may also be appropriate.
In an advantageous embodiment of the invention, the ignition timing, the beginning of injection and the duration of injection are determined as a function of external pressure and external temperature in order to adapt the air volumes supplied to the combustion chambers to the given ambient conditions.
During steady-state operation of the internal combustion engine, preferably an average injection duration is determined, which, using a proportional factor, is converted into an average load value, which is compared with the momentarily set load. The difference between the set load and the average load value is taken into account for ignition and injection and, in particular, also for the air supply. As a result, abrupt changes in the set load do not abruptly affect ignition, injection timing and air supply, but rather are passed on in smoothed fashion, as a result of which, overall, a more harmonious response behavior of the internal combustion engine is achieved.
Further advantages of the invention will become apparent from the following description on the basis of the accompanying drawings.